1. Field of the Invention
The present invention relates to an electronic endoscope suitable for industrial or medical use.
2. Description of the Prior Art
When operating an electronic endoscope which incorporates a solid-state image pickup device at the tip of the probe thereof, it must be adjusted in advance so that best images can be reproduced. The adjustment of image quality is especially important with regard to medical electronic endoscopes because reproduced images are often used as materials for diagnosis.
Conventionally, the adjustment of an electronic endoscope in use is carried out beforehand by controlling white balance, at most, so that optimum images are reproduced. The white balance is adjusted by picking up a white sheet or the like as described in Japanese patent application laying-open No. 61-96891. Other fine adjustments such as gamma balance, black level, flesh-color, or blood color adjustment have not been performed.
The conventional electronic endoscopes have the following problems:
(1) Generally speaking, sizes of test-pattern charts which are used for adjusting electronic endoscopes are very small, for example about 23mm .times.30mm for a small one, although the sizes vary in accordance with objective lenses incorporated in the tips of probes. As a result, image frame alignment between the tip of a probe of an electronic endoscope and a test-pattern chart which is performed by adjusting the distance or the angle between the tip of the probe and the test-pattern chart is very difficult.
(2) Accurate adjustment of an electronic endoscope is often hampered by external light added to the light from a light source. More specifically, the light emitted from the light source is generally transmitted from a video processor to the tip of the probe along the light guide so that the light is emitted from the tip of the probe to an object to be picked up. It is preferable that images be picked up by using this light alone. In practice, however, external light is often added to the light from the light source, thus preventing the accurate adjustment.
For these reasons, it is difficult for conventional electronic endoscopes to incorporate the test-pattern charts necessary for the fine adjustment of image quality. As a result, conventional electronic endoscopes cannot achieve the preliminary adjustment of the image quality. Furthermore, since the conventional electronic endoscopes are not provided with test-pattern charts, they cannot deal with the characteristic degradation of the video system or the light system thereof caused by deterioration with age. Consequently, they must be used without correcting the characteristic deterioration.